A. Field of the Invention
This invention relates generally to the field of ice machines making flake or slurry ice and heat exchangers used in such machines. The invention also relates to a method of manufacturing a heat exchanger for an ice machine.
B. Description of Related Art
Ice is commonly manufactured by even rotational distribution of water around the inside of a vertically-arranged refrigerated cylinder. Another common method is by an even application of water on the outside of a rotating refrigerated drum. The water freezes on the refrigerated surface forming an ice film. The ice film thickness and ice production rate are determined by the water application rate, rotation speed, and the rate at which the refrigerated surface absorbs the heat from the water as ice is formed. A reamer, scraper or like device cracks or otherwise removes the ice from the refrigerated surface, clearing the drum (or cylinder) ahead of the water application, thus continually forming and removing ice (typically in the form of flakes or chunks) as the drum or water application and reamer arm rotates.
Slurry (soft ice) is commonly formed inside a refrigerated heat exchanger cylinder filled with water where a dasher or other device removes ice crystals and/or sub-cooled water from the refrigerated surface before an ice film develops.
The drum (or cylinder) of the above types of ice machines is a heat exchanger and includes an internal passage or internal passages for circulation of a refrigerant. Heat is transferred from the water through the walls of the drum or cylinder to the refrigerant.
The prior art in the art of ice machines includes the following U.S. patents: Goldstein, U.S. Pat. Nos. 6,056,046, 6,286,332; 5,884,501 and 4,796,441; Lyon, U.S. Pat. No. 5,157,939; Gall et al., U.S. Pat. Nos. 5,918,477 and 5,632,159; Tandeski et al., U.S. Pat. No. 4,739,630; Jensen et al., U.S. Pat. No. 5,522,236; and Yundt et al., Jr., U.S. Pat. No. 6,477,846.
In machines designed for producing ice, the refrigerated drum or cylinder is commonly the most expensive part of the machine to manufacture. Additionally, the drum or cylinder is often classed as a pressure vessel and subject to strict manufacturing standards embodied in manufacturing codes, and regulatory oversight and inspections. These regulations and manufacturing standards are in place to provide protection from the hazards of pressure vessels exploding under the internal pressure of the refrigerant. Pressure vessel wall thickness must be adequate to withstand the pressures they are subject to and to meet the safety factors stipulated by pressure vessel manufacturing standards. Increased wall thickness between the refrigerant contained inside the vessel and the water freezing on the external surface of the drum or cylinder increases material cost and impedes heat transfer, reducing the efficiency of the ice production.
In many applications, a relatively non-corrosive material such as stainless steel is required for the ice forming surface. In larger ice machines, this surface may be ¾″ thick, or even thicker, to provide the necessary strength, greatly increasing cost and reducing heat transfer. To compensate for this reduced heat transfer, a lower refrigerant temperature is required for a given ice production rate, which in turn requires larger, more expensive refrigeration machinery and more energy input per unit of ice production.
Another method of manufacturing refrigerated drums or cylinders for ice production not subject to pressure vessel construction codes include machining refrigerant passages in a thick walled cylinder, then skinning it with an interference fitting secondary cylinder, thus creating refrigerant passages. Another method is by lining the inside or outside of the ice producing surface with tubing or fabricated passages creating refrigerant channels where cold refrigerant cools the ice-producing surface. These methods are labor intensive, involve relatively high material costs, and suffer from relatively low heat transfer rate and energy efficiencies.
This disclosure overcomes the deficiencies of the prior art by providing an ice machine, heat exchanger for an ice machine, and methods of manufacturing the heat exchanger which provides for high heat transfer efficiency, reduced labor and materials costs in construction, and does not require that the drum or cylinder in the machine meet pressure vessel construction codes. The ice machine and manufacturing methods of this disclosure reduce ice machine size and manufacturing costs, as well as reduce accompanying refrigeration system size, cost, and operating costs for the machine.
A further aspect of this disclosure also describes methods and ice machines which increase the efficiency and ice production rate for a given drum size by utilizing both the inside and outside surface of the ice-forming cylinder or drum for ice production. The disclosed utilization of both the inside and outside surface can be applied to conventionally constructed drums (e.g., those manufactured as a pressure vessel), as well as the improved heat exchanger drums of this disclosure.